i personally met my co-founders through super smash brothers: melee and during college (separate occasions). we've been good friends for over 4 years, most likely due to our similar interests.

i agree with your post that you should not rush or force yourself to find a co-founder. for those sole founders, i recommend attending mixers to meet people with similar interests and approaching people without the intent of finding a co-founder. make true friendships instead; your co-founders/life partners will follow.